Many processes require an initiation stimulus to start a reaction by releasing heat, and a device to achieve this goal is a critical system component for many processes, such as combustion processes. For combustion processes many different ignition methods exist, the most popular being an electric spark igniter. However, spark igniters require high-energy input supplied by a high-voltage circuitry and by its nature is a single-point stimulus method. Other ignition methods, such as plasma jet injection or flame jet initiation and high-power laser ignition, are all bulky, heavy, and expensive to operate.
There have been some recent reports of optical ignition of carbon nanotubes in oxidizing ambient gases, such as in air. For example, researchers have reported that single-walled carbon nanotubes ignite when exposed to a conventional photographic flash (Ajayan et al., “Nanotubes in a Flash-Ignition and Reconstruction”, Science, Vol. 296, Apr. 26, 2002). This photoeffect is disclosed to occur for single-walled carbon nanotubes prepared by carbon arc, laser ablation, or chemical vapor deposition techniques upon exposure to a camera flash at close range. Ignition and burning is reported to occur when local increases in temperature are sufficient to initiate the oxidation of the carbon and propagate as more heat is released by the exothermic reaction. Heat confinement in nanostructures can thus lead to drastic structural reformation and, under oxidizing environments, induce ignition under conditions not expected for bulk materials. The heat pulse is created by light absorption by the nanotubes from a proximal light flash.
Applications of optical heating or ignition of carbon nanotubes are limited by several characteristics of carbon nanotubes that include size, high aspect ratio, insolubility in water or other liquids, and lack of biocompatibility. Compositions are needed that provide radiation induced heating or ignition in water or other liquids as well as air, have small size and low aspect ratio, and are miscible in a host of materials such that the properties of the materials can be altered by thermal transitions that are promoted photochemically. Moreover, compositions that are biocompatible would allow their use in medical applications.